Partial combustion or gasification of coal involves reaction of the coal at elevated temperatures, and possibly elevated pressures, with a limited volume of oxygen, the reaction preferably being carried out in a reactor or reaction chamber or vessel into which coal is fed by means of "burners" together with additional agents such as steam, carbon dioxide, or various other materials. Gasification of coal produces a gas, known as synthesis gas, that contains mostly carbon monoxide and hydrogen. Also produced are varying minor quantities of other gases, such as carbon dioxide and methane, and, at least with some coals, various heavier materials, such as small sticky or molten particles. The sticky or molten particles are principally alumina-silica minerals present in the coal, and depending on their size and character, are recovered in different ways. In at least one coal gasification process undergoing development, the design of the gasifier is such that a rough separation of the molten particles takes place in the gasifier vessel or reaction space chamber. That is, the heavy particles tend to remain or drop to the bottom of the gasifier vessel to a slag recovery area or bath, and lighter and molten particles are partly deposited by turbulence on the walls of the vessel and partly carried by the synthesis gas upward and out of the reactor chamber into a quench zone which is mounted generally above the gasifier, and wherein a cool quench gas is employed to quench the gas and particles. Nevertheless, the solidified material, because it is derived from a "reducing" atmosphere, may be different in composition and properties from flyash or slag normally associated with combustion boilers, wherein a fully oxidizing atmosphere is utilized. For example, the slag from processes from partial combustion of coal may contain elemental iron, a component not normally associated with boiler slag.
An important aspect of coal gasification processes is the recovery of great quantities of heat, preferably in the form of high grade steam. While the gasifier vessel might appear to be the appropriate location for this recovery, in fact, the case is otherwise. For example, in those cases where the gasification is carried out utilizing burners in an enclosed vessel, the heat of the gasification reaction is so intense that insulating liner materials must be utilized to protect the vessel walls. The designer is thus faced with this dilemma: if heat exchange is too great, the gasification zone will be too cool for good gasification, and the efficiency of the reaction will suffer, while if heat exchange is insufficient, i.e., if heat is allowed to build up, the materials of the gasification zone wall or walls will begin to suffer damage, particularly from combination of high temperature and the reactive components in the synthesis gas.
To overcome this problem, liners, such as those described in U.S. Pat. No. 4,818,224, and suitably treated as specified therein, may be employed. However, the liners are also attacked by the highly corrosive combustion gases and by the molten mineral particles. The invention addresses this problem in a unique manner.